1. Field of the Invention
The present invention relates to a projection apparatus and optical ranging method.
2. Description of the Related Art
Today, a data projector as a projection apparatus for projecting onto a screen an image displayed on a screen of a personal computer, image of a video signal, image from image data stored in a memory card etc., and the like is heavily used.
A projection apparatus often uses a light source which is compact with high intensity, such as a metal halide lamp or extra high pressure mercury lamp, and light output from the light source is irradiated to a display element called liquid crystal or digital micromirror device (DMD) by the optical system of the light source as three primary colors through a color filter to project the transmitted light or reflected light of the display element onto the screen through a group of lenses which are to be the optical system of the projector including a zoom function.
In such a projection apparatus, when a projection plane is in a slanted position to a plane perpendicular to an optical axis of a projected light emitted from the projection apparatus, trapezoidal distortion of the projected video occurs. For example, Japanese Patent Application Laid-Open Publication No. 2005-39558 proposes a technique of measuring a distance from a plurality of points on the projection plane to the projection apparatus with a ranging sensor acting on a phase difference method in order to obtain a relationship of a relative position between the projection apparatus and the projection plane, and based on the result, correcting the trapezoidal distortion in the projected image by image processing without physically adjusting the relationship of the relative position between the projection apparatus and the projection plane.
Japanese Patent Application Laid-Open Publication No. H7-84045 proposes a technique of measuring using a ranging sensor acting on a laser method instead of a ranging sensor acting on a phase difference method, and merits of this technique is that compared to the phase difference method, the ranging speed is faster, the ranging accuracy is higher, etc.
However, in ranging to the projection plane with a laser method performed by a projection apparatus, there is a problem of when an image with a color element having a same wavelength as the laser beam is projected on the projection plane, the influence of the reflected light of the image itself causes reduction of the ranging accuracy.
An object of the present invention is to provide a projection apparatus and an optical ranging method which can measure a distance from a projection apparatus to a projection plane fast and highly accurately.